Pressure transducer apparatus adapted to measure engine pressure parameters

ABSTRACT

A pressure header assembly has a closed front and back surface. The back surface has an aperture for accommodating a separate dual die pressure header. The dual die pressure header has an absolute and differential pressure sensor positioned thereon. A differential pressure port is located on a side surface of the pressure header assembly and is directed to a bore in the pressure header assembly. The bore contains an elongated tube which is positioned in the pressure header assembly and locked in place by means of a crush nut and locking nut assembly. One end of the tube is coupled to the differential pressure port, while the other end of the tube accommodates a differential pressure tube which is bent in an arcuate position and directed to the underside of the sensor of the differential sensor assembly mounted in the dual die pressure header. Suitable leads from the dual die pressure header assembly are directed to a terminal board which is mounted within a pressure transducer housing shell, which terminal board coacts with an outboard contact cap assembly forming the transducer. The pressure header assembly portion also contains extending tabs which have apertures for external mounting.

FIELD OF THE INVENTION

This invention relates to pressure transducers in general and moreparticularly to a pressure transducer apparatus adapted to measureengine pressure parameters including the pressures at the engine fueland oil filters.

BACKGROUND OF THE INVENTION

Pressure transducers have been widely employed in many environments inorder to monitor pressure. Such environments include very harshenvironments such as monitoring pressure in automotive internalcombustion engines, aircraft engines as well as in other environmentswhich are subjected to relatively high pressures and high temperatures.It is desirable to monitor engine pressures in order to determine properoperation of an engine during extreme conditions. These engines can ofcourse be automotive engines, or aircraft engines as well as enginesutilized in missiles or in other devices.

A purpose of taking pressure measurements in conjunction with engines isto determine the fuel and oil filter pressures and thus, to providepressure data that will be used to determine important engine filtermaintenance. As one can ascertain, especially in regard to aircraftengines, the measurement of pressure regarding the engine fuel filterand oil filter pressures involve relatively high temperatures as well ashigh pressures.

Pressure is determined in terms of an absolute pressure, so that theabsolute pressure can be monitored to determine overall engineperformance and also to determine when the filters need to be replaced.This can be done by utilizing the pressure measurements obtained fromthe pressure transducer and applying such measurements to amicroprocessor or other computing device to determine when pressuresfall outside a desired range and therefore to make some determination ofwhether the filters have to be replaced.

In order to facilitate such measurements, it would be desirable toreduce the number of pressure transducer assemblies required todetermine such operation. Cognizant of this problem, the prior art wouldutilize two independent absolute measurements for each filter. Onepressure transducer would be upstream of the filter and one pressuretransducer would be downstream of the filter. In this manner there wouldbe four transducers utilized per engine. In order to reduce the numberof transducers, the present approach enables one to mount twoindependent sensors into two different transducers. In this manner thefuel filter transducer would measure pressure both upstream anddownstream and the oil filter transducer would perform the samefunction.

The apparatus according to embodiments of the present invention wouldallow two less transducers per engine and result in a reduced interfacepiece per count at a reduced weight and lower cost.

Use of two pressure sensors in one transducer is described in, forexample, U.S. Pat. No. 6,272,928 entitled “Hermetically Sealed Absoluteand Differential Pressure Transducer” issued on Aug. 14, 2001 to A. D.Kurtz, and assigned to the assignee herein Kulite SemiconductorProducts, Inc. That patent depicts a single semiconductor chip whichincludes dielectrically isolated leadless pressure sensors adapted tosimultaneously measure a first pressure and a differential pressurebetween the first pressure and a second pressure. The chip includes awafer, which includes first and second recessed portions defining firstand second diaphragm areas. There is a rim portion formed between thefirst and second recess portions for isolating the first diaphragm fromthe second diaphragm. A first circuit is mounted on the first diaphragmand responsive to the first pressure and a second circuit is mounted onthe second diaphragm and responsive to the second pressure. The firstand second circuits can be electrically coupled to one another so as tocooperatively provide a common output indicative of differentialpressure associated with the first and second pressures, whilesimultaneously providing an output indicative of either the first orsecond pressures.

FIG. 1 of the above-noted patent illustrates a plan view of a sensorstructure formed on a single wafer. The structure includes twoindependent open four active arm Wheatstone bridges each having sixcontact areas or fingers respectively. Each bridge has its own activearea defined by an associated deflectable diaphragm. Open bridges aredepicted in FIG. 2 of the patent and the various bridge configurationscan be interconnected to provide an output proportional to the pressuredifference between a first and second pressure as well as providing anoutput indicative of the first and second pressures. Also indicated inthat patent are other instances where it is necessary to simultaneouslymeasure both the absolute and differential pressure. Such devices can beused to determine aircraft speed where speed is measured by measuringthe total pressure which is the pressure against the nose of theaircraft as it moves through the air and the static pressure which isthe atmospheric pressure surrounding the aircraft. The air speed isproportional to the difference between a total and static pressure. Seealso U.S. Pat. No. 6,612,179 issued on Sep. 2, 2003, entitled “Methodand Apparatus for the Determination of Absolute Pressure andDifferential Pressure Therefrom” to A. D. Kurtz, and assigned to KuliteSemiconductor Products, Inc. That patent depicts a combination absoluteand differential pressure sensing device, which includes a plurality ofabsolute pressure transducers, each transducer including a plurality ofhalf-bridge piezoresistive structures. The device selectively couples atleast one of the plurality of half-bridge structures through a first oneof the absolute pressure transducers to form a half active full bridgestructure adapted to measure an absolute pressure. At least one other ofthe plurality of half bridge piezoresistive structures is connected toat least one of the half bridge structures of a second absolute pressuretransducer to form a full bridge adapted to measure a differentialpressure. The structure is depicted in FIG. 1 and FIG. 2 of the abovepatent, with various circuit configurations depicted in FIGS. 3-6. Seealso U.S. Pat. No. 7,057,247 entitled “Combined Absolute DifferentialTransducer” issued on Jun. 6, 2006 to A. D. Kurtz et al and assigned tothe assignee herein. That patent describes a combined absolutedifferential pressure transducer which consists of two sensors made fromthe same silicon wafer. The patent shows both separate absolute anddifferential sensor wafers or dies as well as a single wafer or diecontaining only an absolute and differential pressure sensor.

Although prior patents illustrate providing two pressure sensors in asingle pressure transducer structure, it is however, desirable toprovide an improved pressure transducer assembly for monitoring engineparameters such as fuel and oil filter pressure values in an engine, ina simplified and economical manner and with high temperature operation,in a relatively small and rugged device.

SUMMARY OF THE INVENTION

A pressure transducer apparatus, comprising: a pressure transducerheader of a cylindrical shape and having closed front and back surfaces,with the front surface having a main pressure port opening, the openingextending from the front surface towards the back surface, the backsurface having a pressure die accommodating opening therein whichopening communicates with the pressure port opening, a differentialpressure port opening on a side surface of the pressure transducerheader, a bore having an opening in the back surface and extendingtowards the front surface, with the differential pressure portcommunicating with the bore, a die accommodating header having topsurface and a rear surface, the header of a shape corresponding to theshape of the pressure die accommodating opening with the dieaccommodating header to be inserted therein, the die header having afirst set of terminal apertures on the top surface extending to the rearsurface, a second set of terminal apertures on the top surface alsoextending to the rear surface, the second set of terminals surrounding adifferential pressure port opening which opening extends from the topsurface of the die header to the bottom surface, terminal pins insertedinto the terminal apertures to extend from the top surface and directedto the rear surface and to extend beyond the rear surface, a firstpressure transducer die positioned on the top surface of the die headerand connected to the first set of terminal pins, a second pressuretransducer die positioned on the top surface and connected to the secondset of terminals, each of the pressure transducer dies having adeflectable diaphragm and having located thereon pressure responsivesensors which vary resistance according to an applied pressure, adifferential pressure tube extending from the bore opening in the rearsurface of the pressure transducer header to the differential portopening of the die header, where when a first pressure is applied to themain pressure port opening both pressure transducer dies receive thefirst pressure, and when a second pressure is applied to thedifferential port only the second pressure transducer receives thepressure, so that the first pressure transducer provides an outputindicative of the absolute value of the first pressure with the secondtransducer providing an output indicative of the difference between thefirst pressure and the differential pressure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view taken through line 1-1 of FIG. 2depicting a pressure transducer assembly according to an embodiment ofthe invention.

FIG. 2 is a top plan view of the pressure transducer assembly.

FIG. 3 is a cross-sectional view taken through line 3-3 of FIG. 4depicting a dual die header assembly for accommodating an absolute anddifferential pressure sensor die according to an embodiment of theinvention.

FIG. 4 is a top plan view of the header assembly depicted in FIG. 3.

FIG. 5 is a perspective view of a pressure header assembly according toan embodiment of the invention.

FIG. 6 is a perspective view of a dual die header assembly according toan embodiment of the invention.

FIG. 7 is a perspective view of the dual die header assemblyaccommodating a differential and absolute pressure assembly and areference tube according to an embodiment of the invention.

FIG. 8 depicts the dual die pressure header of FIG. 7 mounted on thepressure header of FIG. 5.

FIG. 9 is a perspective view depicting the pressure transducer assemblyas shown in FIG. 1.

FIG. 10 is a cross-sectional view of a typical pressure sensor employingpiezoresistive sensors which can be employed in conjunction withembodiments of the invention.

FIG. 11 is a cross-sectional view of a differential pressureaccommodating tube used in embodiments of the invention.

FIG. 12 is a top view of a lock nut structure employed in embodiments ofthe invention.

FIG. 13 is a cross-sectional view taken through line 13-13 of FIG. 12.

FIG. 14 is a top view of a crush nut assembly employed in embodiments ofthe invention.

FIG. 15 is a cross-sectional view taken through line 15-15 of FIG. 14.

FIG. 16 is an assembly view showing the complete assembly of adifferential pressure accommodating tube utilized in embodiments of theinvention and utilizing the components shown in FIGS. 11-15.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, there is shown a header which is an integralpart of the pressure transducer assembly to be described. EssentiallyFIG. 2 shows a top-plan view of the pressure transducer header accordingto an embodiment of the invention. The header 10 has a cylindrical frontportion with a closed top surface 23 and a closed rear or bottom surface24.

The cylindrical header 10 has extending tabs 11 and 12 near the rearsurface 24. The tabs extend radially from opposing side surfaces of theheader 10. Each tab 11 and 12 has an aperture 13 and 14 in order tosecure the transducer in a suitable position. The transducer header 10has a pressure port 15, which receives a reference or absolute pressure.The reference pressure can be the pressure which exists in a fuel lineof an automotive engine or some other pressure source and basically willbe referred to as a reference or absolute input pressure.

FIG. 1 is a cross-sectional view taken through line 1-1 of FIG. 2. Thus,as seen in FIG. 1, the extending tabs or extending flanges 11 and 12 areshown in cross-sectional view with their accommodating apertures 13 and14. The pressure port 15 has a front opening on the front surface 23 ofthe cylindrical pressure transducer header 10 extends through a bore 44in the header housing 10. The bore 44 enters a cavity 41. In cavity 41as will be explained, is positioned a dual die header assembly 30, whichheader assembly 30 accommodates an absolute and differential pressuretransducer or die. Each pressure die contains a full Wheatstone bridgeand is operative to produce a voltage output when a pressure is appliedto a deflecting diaphragm surface of the pressure transducer or pressuredie.

As seen in FIG. 1, the cavity 40 contains the header assembly 30 whichcontains an absolute and differential pressure assembly. The headerassembly 30 further has leads 53, 54 which are directed to a terminalboard 26. There are conventionally four leads from each die as leads 53,54, which are directed to the terminal board 26 to enable one to biasand obtain output signals from the transducers.

In the embodiment of FIG. 1, header 10 has a differential pressure portinput 21 in the side surface of the header. Input port 21 is directed tointerface with a bore 38. The bore 38 is directed to a tube 33associated with a lock nut structure 32 and a crush ring 34. The lockring or lock nut 32 is positioned in an aperture 45 within the header10. The aperture 45 also contains the crush nut 34. As the lock nut 32is pushed into the housing, the crush nut impinges on the sides of theheader 10 about aperture 45 which crush nut firmly seals the assembly inthe aperture 45. The tube 33 is held by the lock nut and crush ring andis also firmly secured. The crush nut 34 forms a tight seal from thedifferential port without the need for welding, soldering and so on.

As seen in FIG. 1, the tube 33 associated with the above-noted lockingassembly and which is associated with the differential input port 21,has a further reference tube 31 coupled to an output. The tube 31 isinserted at one end into the bore of tube 33 and has an arcuate bend toenable the tube 31 to extend into the header 30. This tube 31 suppliesthe differential pressure to the underside of one of the diaphragm areasof the die located within the header 30.

Also shown in FIG. 1, is a filter 40, which filter, may or may not beincluded. If included, the filter 40 operates to filter or removeparticles or contaminants which may be carried by the pressure mediumand which may enter bore 44 via port 15 during operation.

As seen in FIG. 1, a differential pressure P_(d) is applied to the port21, while the reference or absolute pressure P_(R) is applied to port15. As previously indicated, pressure P_(R) for example, may be a fuelpressure in an engine or an oil pressure in an engine while the pressureP_(d) (the differential pressure) may be the pressure on the other sideof the fuel filter or on the other side of the oil filter. In thismanner, as will be described, one of the sensors contained in the headerassembly 30 will produce an output which is the difference of pressurebetween P_(R) and P_(d). This differential pressure enables anautomotive manufacturer to determine the pressure difference between forexample, the input and output of a filter. It is indicated that such atransducer can be used to monitor oil pressure data or fuel pressuredata.

Also seen in FIG. 1, the pressure header assembly 10 has O-rings 20 and22 which each are retained within a circumferential bore about the topportion of the pressure header 10 to enable mounting or insertion into asuitable aperture where a pressure is to be monitored. Thus theabove-noted header 10 as described mainly contains a differential and areference pressure port and contains an opening 41 to accommodate a dualdie header 30. The term dual die header is utilized to indicate that theheader 30 contains an absolute and a differential pressure die, whichessentially is an absolute pressure Wheatstone bridge and a differentialpressure Wheatstone bridge.

The header 10 is now coupled to an external cylindrical shell 25 whichis secured to the header 10 and which contains the terminal board 26.The cylindrical shell 25 surrounds and protects the leads 53, 54 andterminal board 26. The terminal board 26 as seen in FIG. 1 is mountedwithin the cavity of the outer shell 25. The outer shell 25 alsocontains an output aperture which accommodates an output capping member28. The capping member or cap 28 contains contacts 27 which interfacevia connections or wires 35 with contacts 48 on the terminal boardassembly. This contact assembly or header 28 is utilized to interfacewith external devices. In this manner all of the output leads for thepressure transducers which are contained within the header 30 aredirected via the terminal board 26 to contacts 27 to the output apertureof cap 28. The pressure sensors can receive biasing voltages while theoutput of the Wheatstone bridges can also be directed through theterminal board and hence, through the output connectors. The shell 25has the front opening inserted into the flanged channel 26 of the header10.

Now referring to FIGS. 3 and 4, there is shown the double die header 30depicted in FIG. 1. FIG. 4 shows a top-plan view of the header 30 asshown in FIG. 1. The header 30 has a peripheral flange 59 and as seenfrom the top-plan the header 30 has two area locations 57 and 58. Eachlocation 57 and 58 has four apertures arranged in a circular pattern, asillustrated by aperture 61 associated with area 57, and aperture 60associated with area 58. There are four apertures associated with areas57 and 58 and they are arranged in a circular pattern. Area 57 furtherhas an opening 62 which is a differential pressure input. The opening orinput applies the differential pressure to the back of a deflectingdiaphragm associated with the differential wafer die while the front ofthe diaphragm receives the absolute or reference pressure. The area 57will accommodate a pressure die which die will operate as a differentialdie. In the embodiment of FIG. 4, each of the four apertures 60, 61associated with areas 58, 57, respectively, are uniformly arranged in acircular configuration. As shown in FIG. 4, opening 62 is positionedcentral to the apertures 61 within the area 57.

The tube 31 (FIG. 1) which is associated with the differential pressureport 21 terminates within opening 62 of the header 30. This tube asindicated, supplies a differential pressure to the underside of thedifferential die or diaphragm. The absolute or reference pressure willbe applied to the top surface of a die which is located in area 58. Thisdie is referred to as an absolute die and receives the referencepressure P_(R) via the bore 44 as seen in FIG. 1. It is also noted, thatthe die associated with area 57 or differential die also receives thepressure P_(R). Therefore, the differential pressure sensor will producean output pressure indicative of the difference of P_(R) and P_(d). Theabsolute pressure will produce an output pressure strictly in accordancewith the pressure P_(R) as applied thereto.

As one can also understand, the actual semiconductor dies can basicallyconstitute a single die which contains two full Wheatstone bridges. Thedie would be placed within the header on top of the areas 57 and 58where contacts from the die will be directed through the suitableapertures such as 60 and 61.

It is preferable that two separate dies be employed in mostapplications. The reason for two separate dies is that the pressureP_(R) may be a very large pressure as compared to P_(d) (or vice versa).Even though the differential pressure as exhibited by one die will beless, as it is the difference between P_(R) and P_(d) and therefore thewafer diaphragm can be thinner, it is understood that if thedifferential pressure source fails, the diaphragm may rupture.Therefore, it is preferable to employ two different dies so that one mayutilize a thinner diaphragm for the differential transducer while alsoassuring that this diaphragm will not rupture in the event that thedifferential pressure source fails and therefore only the absolutepressure is applied (or vice versa).

FIG. 3 is a cross-sectional view of FIG. 4 taken through lines 3-3. Asseen, the cross-sectional view of FIG. 3 is analogous to thecross-sectional view of the header 30 depicted in FIG. 1. As seen theheader 30 has the peripheral flange 59 which enables it to be mountedwithin the area 41 of the pressure header structure 10 of FIG. 1. Theareas 57 and 58 are shown with contacts positioned within the apertures.Contact terminals 52, 53 and 54 are each positioned within an apertureas for example apertures 60, 61.

Also shown is the reference tube 31 directed into the aperture 62associated with the header 30. The reference tube 31 supplies thedifferential pressure to the underside of an active diaphragm areaassociated with a die and which die will be positioned over the area 57in the case of a differential die and over the area 58 in the case of anabsolute die.

Before proceeding with further explanation, reference is made to theabove noted U.S. Pat. No. 7,057,247 which issued on Jun. 6, 2006, to A.D. Kurtz et al, and assigned to the assignee herein. That patent isentitled “Combined Absolute Differential Transducer” and shows acombined absolute and differential pressure transducer which basicallyconsists of two sensors made from the same silicon wafer and is selectedto be adjacent to each other on the wafer. The sensors can be individualdies which basically are fabricated during the same process on thesilicon wafer.

In this manner, both sensors are very closely matched both thermally andotherwise. The same pressure which is the P_(R) is applied to one sideof both sensors and a second pressure, which is the differentialpressure, is applied via the tube 31 to the differential sensor to causethat sensor to produce an output indicative of the difference betweenpressures. This aspect of operation and structure is described in U.S.Pat. No. 7,057,247, the entire specification and disclosure of which isincorporated by reference herein as if fully recited herein. The patentexplains how to select dies or pressure transducers with the samediaphragm thickness but which may have different size active areas wherethe thermal coefficients and thermal sensitivities are controlled by thepurity and concentration of the P regions of the sensors and by how wellthey match each other.

Thus, as in the present invention, thermal properties of two individualsensors are closely controlled and matched to each other, which resultin an improved overall combined absolute and differential transducer. Amajor aspect of the present invention relates to the housing structuresto accommodate the sensors in a convenient and compact package, which isrugged and therefore capable of operating in harsh environments.

In the above-noted U.S. Pat. No. 7,057,247, FIGS. 7A and 7B show aheader structure which is similar to the header structure 30 withoutcertain of the mechanical characteristics employed in this invention.FIGS. 7A and 7B of that patent show an absolute and a differential diemounted on the header. FIG. 7C shows a cross-sectional view. It isunderstood from the above patent that the differential and absolute diescan be separate dies, or separate wafers or can be employed on a singlewafer.

Again referring to FIG. 3, the cross-sectional view of the wafer shownalso has a glass header 55 which serves as an insulator. The header 55accommodates the pins as well as the reference tube and serves toinsulate the semiconductor dies from the environment. Such a header isshown in above-noted U.S. Pat. No. 7,057,247 in FIGS. 8A-8D. In thatpatent FIGS. 6A and 6B show single dies which may be employed for theabsolute and differential pressures while FIG. 6C shows a single diehaving a both an absolute and a differential pressure sensor positionedthereon. Either configuration can be employed. However, it is preferredto utilize separate dies for the differential and absolute structures.

Referring to FIG. 5, there is shown a perspective view of thecylindrical pressure transducer header assembly 10 as depicted inFIG. 1. As seen from FIG. 5 the same reference numerals have beenutilized to designated like parts. There is shown the extending flanges11 and 12 with their associated apertures 13 and 14. The referencenumeral 38 refers to the bore 38 of FIG. 1, which extends through thetube 33 and which will eventually accommodate the reference tube 31.Tube 31 brings the differential pressure to the underside of thedifferential die. Opening 41 eventually receives the header 30 and thereis shown the differential pressure port 21. FIG. 6 depicts a perspectiveview of the header 30. In FIG. 6 the same reference numerals have alsobeen utilized to designate the same parts.

Also seen in FIG. 6 is the contact or leads 53, 54 which are coupledthrough the apertures in the header. The area 58 of the absolutepressure die which receives pressure P_(R) is depicted. The area orposition 57 of the differential die is also depicted. FIG. 6 provides amore detailed illustration of the structure of the header 30 as depictedin FIGS. 3 and 4. Referring to FIG. 7, there is shown the header 30 withthe reference tube 31 bent in an arcuate shape and coupled to opening 62(FIG. 4).

Also shown in FIG. 7 is a differential die 70 positioned to receive afirst pressure at the top side which is the pressure P_(R) and toreceive the differential pressure Pd via tube 31 at the bottom side ofthe diaphragm. The absolute die or device 72 receives the pressureP_(R), as shown for example in FIG. 1.

In FIG. 8 there is shown the header 30 mounted within the aperture 41 inthe header 10 as depicted in FIG. 1. Also shown in FIG. 8 is a lockwasher or lock nut 80 which firmly secures the reference tube 31 to thepressure header housing 10. Again similar reference numerals have beenutilized to depict similar structures. It should be clear to one skilledin the art of the mechanical nature of the structures constituting theheader for the die as well as the overall pressure header according tothis invention.

Referring to FIG. 9 there is shown the pressure header 10 accommodatingthe dual die header 30 with the reference tube 31. Shell enclosuremember 25 contains the terminal board 26 as well as the contact areas.This is associated and shown with the cap member 28. Cap member 28 hasan output aperture designated by reference numeral 91 through whichwires or leads may be directed to an external source for operation ofthe device. The housing and structure described herein contains anabsolute and differential pressure sensor. Each pressure sensor is aWheatstone bridge consisting of four piezoresistors secured to asemiconductor substrate. Such devices are well known in the art.

Referring to FIG. 10, there is shown a typical silicon sensor whichbasically can function as the absolute or differential die as describedherein. In one configuration, silicon sensors are packaged into apressure capsule designated as a header such as 101 to allow mechanicaland electrical packaging of sensors into various environments. Thesensor shown in FIG. 10 can be used as the differential or absolutesensor, also referred to as dies, as depicted, for example, in FIG. 7 as70 and 72.

As shown in FIG. 10 a silicon chip 91 has a diaphragm area 100. The chip91 is inorganically bonded to a special cover wafer with the holesstrategically drilled in the cover. The cover wafer can be a glasscontact wafer such as 98. The silicon chip 91 has a layer of silicondioxide 92, which silicon dioxide layer 92 serves as an insulator and isbonded to the glass contact wafer 98. P type diffused monocrystallinesilicon piezoresistors 95 are positioned beneath the thin diaphragmareas 100 of the sensor chip. Contacts to the piezoresistors are madethrough metal contact areas as 97 which are connected to contact pins as93 through a metal to glass frit conductive substance 96. The electricalcontact is made using this high temperature metal frit which istypically a mixture of high conductivity metal in appropriate physicalform and glass. The frit is used to fill the holes in the cover waferand the leadless pressure capsule is bonded to a specifically designedheader at a high temperature using a conductive glass frit. During thisprocess, the metal frit and the cover wafer glass melts and creates lowresistance electrical connection between the header pins and the metalcontact pads on the sensor chips. Only the non-active side of thediaphragm is exposed to the pressure medium for the absolute transducer.

This structure depicted in FIG. 10 of course can be utilized for boththe absolute and differential transducers. It is understood that for thedifferential transducer a further hole is required to interface to theunderside of the diaphragm to apply the differential pressure thereto.This structure and configuration is depicted in the above-noted U.S.Pat. No. 7,057,247. Reference is also made to the above-noted U.S. Pat.No. 6,612,179 entitled “Method and Apparatus for the Determination ofAbsolute Pressure and Differential Pressure Therefrom” and U.S. Pat. No.6,272,928 entitled “Hermetically Sealed Absolute and DifferentialPressure Transducer”, which show pressure transducers employingWheatstone bridge configurations with either full bridges or halfbridges which can be interconnected to produce absolute and differentialpressure outputs.

In accordance with the principles of the present invention, theformation of the header and the positioning of the absolute anddifferential Wheatstone bridges in the header enable an easy coupling ofboth absolute and differential pressure to the pressure sensing devices.

Referring now to FIGS. 11-16, there are shown structures foraccommodating the differential pressure tube 31. The tube 31 shown inFIG. 1 is an arcuate tube directing the differential pressure port tothe underside of the differential sensor. As seen in FIG. 11 there isshown the tube 33, which tube at one end receives the differentialpressure, which differential pressure is transmitted via the opening inthe tube to the output end of the tube 33. The output end 110 receivesthe one input of the reference tube 31 which is inserted in to the bore120.

Shown in FIG. 12 is a top view of the lock nut section 32. The lock nut32 has a central aperture 111 which again accommodates the tube 33. Thelock nut 32 has a flange at one end coextensive with a shaft 110 whichshaft 110 is directed into the aperture 45 formed within the pressureheader housing section 10 (FIG. 1).

Shown in FIG. 14 is a top view of the crush ring 34. The crush ring 34also has an aperture 112 which accommodates the tube 33.

Referring to FIG. 16, there is shown the assembled apparatus. Asindicated, there is an aperture 45 formed in the pressure header housing10. Into the aperture 45 is inserted shaft 110 of the lock nut 32accommodating the tube 33 with the crush nut 34 located at one end. Thedifferential pressure port 38 is shown therein. Essentially the entireapparatus is forced or pushed into the aperture 45 and in such a mannerthat the crushing ring abuts against the surfaces of the pressure headerhousing 10. The ring is of a soft material and basically is embeddedinto the housing 10 by a pressure or force exerted thereon by the locknut 32. The lock nut 32 may be threaded or otherwise, but in any eventit is turned until very little additional force can be applied. Thiscauses the crush nut to embed within the walls of the aperture 45 formedin the header 10. This allows for an extremely tight assembly which isas strong as a bonding or ordinary mechanical installation and againrequires no bonding materials or welding or any high temperatureoperation in order to fabricate and form the same. Such connection alsoforms a tight fluid impervious seal.

Therefore, in accordance with the above description, there is describeda compact pressure transducer assembly which includes an active anddifferential sensor which are all contained in one header and whichenables one to measure pressures in harsh environments, such as the fueland oil pressure of an engine. The devices employed aresilicon-on-silicon sensor elements which eliminates all p-n junctions.Such junctions would introduce instability and inaccuracy into thedevice, resulting in a wider error band. Thus, without p-n junctionlimitations static error bands of 0.1% to 0.2% are typical.

The silicon-on-silicon sensor converts pressure to an electrical signalby means of the piezoresistive effect. Each of the sensors contain foursilicon strain gauges which are fusion bonded on the surface of amicromachined silicon diaphragm on which a dielectric layer of silicondioxide has first been grown. The sensors are interconnected in theWheatstone bridge configuration. When exposed to pressure, themicromachined silicon diaphragm deflects deforming the silicon straingauges which have a very high rate of change in resistance when appliedto stress. This will result in an imbalance in the Wheatstone bridgewhich imbalance is proportional to pressure measured. Therefore thebridge produces an output which is a voltage output proportional topressure. The pressure header according to this invention has a separateheader which contains the absolute and differential structures. Theabsolute structure is responsive to an absolute or reference pressure.

The differential sensor is responsive to the reference pressure and thedifferential pressure to produce an output which is the differencebetween both pressures. The entire structure is extremely compact andextremely rugged and can be mounted within an engine in variouspositions due to the simple mounting techniques and the structure of theheader in general. Thus it will be apparent to one skilled in the artthat there are many alternate embodiments which may be envisioned, andall of which are deemed to be encompassed within the spirit and scope ofthe claims appended hereto.

1. A pressure transducer apparatus, comprising: a pressure transducerheader of a cylindrical shape and having closed front and back surfaces,with said front surface having a main pressure port opening, saidopening extending from said front surface towards said back surface,said back surface having a pressure die accommodating opening thereinwhich opening communicates with said pressure port opening, and adifferential pressure port opening on a side surface of said pressuretransducer header, a bore having an opening in said back surface andextending towards said front surface, with said differential pressureport communicating with said bore, a die accommodating header having atop surface and a rear surface, said header of a shape corresponding tothe shape of said pressure die accommodating opening said dieaccommodating header to be inserted therein, said die header having afirst set of terminal apertures on said top surface extending to saidrear surface, a second set of terminal apertures on said top surface ofsaid die header also extending to said rear surface, said second set ofterminals surrounding a differential pressure port opening which openingextends from said top surface to said rear surface, terminal pinsinserted into said terminal apertures to extend from said top surfaceand directed to said rear surface and to extend beyond said rearsurface, a first pressure transducer die positioned on said top surfaceof said die header and connected to said first set of terminal pins, asecond pressure transducer die positioned on said top surface of saiddie header and connected to said second set of terminals, each of saidpressure transducer dies having a deflectable diaphragm having locatedthereon pressure responsive sensors, which vary resistance according toan applied pressure, a differential pressure tube extending from saidbore opening in said back surface of said pressure transducer header tosaid differential port opening of said die header, wherein when a firstpressure is applied to said main pressure port opening both said firstand second pressure transducer die receive said first pressure, and whena second pressure is applied to said differential port only said secondpressure transducer receives said pressure, so that said first pressuretransducer provides an output indicative of the absolute value of saidfirst pressure with said second transducer providing an outputindicative of the difference between said first pressure and saiddifferential pressure.
 2. The pressure transducer apparatus according toclaim 1, further comprising: a differential pressure accommodatingapparatus, a supplemental pressure tube, surrounded at a central sectionby a lock nut, said lock nut having a central bore for accommodatingsaid pressure tube, a crush ring having a central bore surrounding saidpressure tube and positioned to contact an end of said lock nut, saidcrush ring having a tapered outer surface which tapers from a smalldiameter at the front of said crush ring to a larger diameter at the endof said crush ring, which larger diameter end contacts the end of saidlock nut, said differential pressure accommodating apparatus insertedinto said bore of said pressure header to cause said crush ring to beforced into said bore, creating a tight pressure seal for saiddifferential pressure.
 3. The pressure transducer apparatus according toclaim 1, further comprising: a cylindrical tubular shell header assemblyhaving a top and bottom opening, a terminal board having contactterminals located in the hollow of said tubular member between said topand bottom opening, said shell header secured to said pressuretransducer header to enclose said die accommodating header, with saidterminal board terminals connected to associated terminals of said dieaccommodating headers.
 4. The pressure transducer apparatus according toclaim 1, further comprising: first and second tabs extending fromopposing sides of said cylindrical pressure transducer header, eachhaving an aperture thereon to enable mounting of said pressuretransducer apparatus.
 5. The pressure transducer apparatus according toclaim 2, wherein said pressure accommodating apparatus comprises adifferential pressure tube connected to one end of said supplementalpressure tube and then coupled to said differential pressure portopening.
 6. The pressure transducer apparatus according to claim 5,wherein said differential pressure tube is bent into an arcuate form tocouple to said differential pressure output port.
 7. The pressuretransducer apparatus according to claim 1, wherein said pressureresponsive sensors are piezoresistive sensors.
 8. The pressuretransducer apparatus according to claim 1, wherein both said first andsecond pressure die transducers are silicon transducers each fabricatedfrom a silicon wafer and having dielectrically isolated piezoresistorson an active area of said wafer.
 9. The pressure transducer apparatusaccording to claim 8, wherein each wafer includes four piezoresistivesensors connected to a Wheatstone bridge array.
 10. The pressuretransducer apparatus according to claim 8, wherein said dielectricisolation constitutes a layer of silicon dioxide formed on said siliconwafer.